THE CARBON DIOXIDE OF THE SOIL AIR 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 



HAROLD WORTHINGTON TURPIN 



SEPTEMBER, 1918 



Reprinted from Memoir 32, AprU, 1920, of Cornell University Agricultural Experi- 
ment Station. 



THE CARBON DIOXIDE OF THE SOIL AIR 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 



HAROLD WORTHINGTON TURPIN 



SEPTEMBER, 1918 



Reprinted from Memoir 32. April, 1 920. of Cornell University Agricultural Experi- 
ment Station. 






LIBRARY Or CONGRESS 

MAR 261921 

DOCUMENTiJ uiV.siON 






CONTENTS 

PAGE 

Historical review 319 

Importance of tlie carbon dioxide in the soil 319 

Factors aiifecting the amount of carbon dioxide in the soil air ... . 321 

Soil organisms 321 

Soil conditions 321 

Seasonal conditions ! 321 

The crop 322 

Chemical factors 323 

Simimary 323 

Experimental work 324 

Experiment 1 324 

Results 328 

Effect of crop 328 

Carbon-dioxide and water relationships 331 

Effect of temperature and atmospheric pressure ....... 335 

Summary of experiment 1 337 

Experiment 2 337 

Results ; 339 

Summary of experiment 2 344 

Experunent 3 344 

Results 345 

Simimary of experiment 3 347 

General summary 347 

Bibliography 349 

Appendix (containing tables) 353 



315 



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THE CARBON DIOXIDE OF THE SOIL AIR 



THE CARBON DIOXIDE OF THE SOIL AIR 

H. W. TURPIN 

Carbonic acid has long been recognized as an important soil solvent. 
On this point, at least, authorities are well agreed, but from the data 
available it is not yet clear what factors are most important in controlling 
the production of carbon dioxide in the soil. It is generally conceded, 
however, that a large proportion of the carbon dioxide found is due to 
soil microorganisms. The significance of plant roots in this connection 
has been recognized by some investigators, while others appear to be not 
quite decided as to how important plant-root excretions are. 

HISTORICAL REVIEW 
IMPORTANCE OF THE CARBON DIOXIDE IN THE SOIL 

That carbon dioxide in solution is an important soil solvent has been 
shown by Stoklasa and Ernest (1909).^ These workers point out that 
when ground gneiss and basalt are mixed with nutrient solutions, the 
amount of phosphorus and potassium absorbed by the plants grown 
is directly proportional to the carbon dioxide produced per gram of dry 
matter of the roots. 

Aberson (1910) concluded, as a result of studies with young plants, that, 
while the excretions from plant roots may not be sufficiently concentrated 
(in carbon dioxide) to have a marked effect in dissolving insoluble materials, 
still the mucilaginous covering of the root hairs, containing a saturated 
solution of carbon dioxide, is entirely sufficient to bring into solution the 
insoluble soil constituents with which it comes in contact, especially the 
phosphates. 

The limited usefulness, as a solvent, of the carbon dioxide secreted by 
plant roots is pointed out by Pfeiffer and Blanck (1912), who show that 
in soils treated with phosphates the carbon dioxide given off by plant 
roots is not a sufficient solvent to account for all the mineral nutrients 
obtained by the plant from the soil. 

1 Data in parenthesis refer to Bibliography, page 349. 

319 



320 PI. W. TuEpm 

Bssides its importance as a direct solvent in the soil, carbon dioxide 
has considerable significance as an indicator of certain soil activities 
Hutchinson (1912) observed a relationship between the biological activi- 
ties and the amount of carbon dioxide in the soil. Russell (1915, a and 
b) noticed a close parallehsm between the carbon-dioxide and the nitrate 
production in the soil, there being more of these constituents in spring 
and fall than in midsummer and winter. It was pointed out later by 
Russell and Appleyard (1915) that the curves for the bacterial numbers 
the nitrate production, and the carbon-dioxide content in the soil thru- 
out the season, show marked simHarity, indicating that the carbon dioxide 
may serve to some extent as an indicator of other soil activities. NeUer 
(1918), however, could find in his experiments no correlation between the 
ammonia production and the carbon dioxide formed, except in cases in 
which he used pure cultures of bacteria. The lack of correlation he 
attributed to the predominating influence of fungi in the soil. 
_ In addition to its importance as a direct solvent in the soil and as an 
indicator of certain soil activities, carbonic acid may possibly be significant 
as an inhibitor of the activity of soil organisms and perhaps even of plant 
growth. Large quantities of carbon dioxide in the air have been found by 
numerous investigators to be detrimental to the growth of the higher 
plants. E. Wollny (1897) observed an increased production of carbon 
dioxide with an increase in the organic matter in the soil, but the increase 
to the umt of organic matter was less with the larger appHcation. This 
Wolhiy attributed to the inhibiting effect of carbon dioxide on the bacterial 
activities. The work of Plummer (191G), however, showed that exceed- 
ingly large amounts of carbon dioxide do not interfere with the activities 
of the ammonifying and nitrifying organisms, provided, in the latter case 
that the oxygen supply is not reduced below a certain minimmn The 
same investigator showed that the maximum carbon-dioxide production 
m the soil corresponds with the point of maximum nitrification In 
studies on the carbon dioxide produced in lysimeter tanks, Bizzell and 
Lyon (1918) noted a marked decrease in the production of this gas after 
the blooming period of an oat crop on Dunkirk clay loam. This decrease 
they say, "was apparently due to the depressing effect of the crop on 
production by bacterial action." Such a decrease was not found to take 
place on a Volusia silt loam. 



The Carbon Dioxide of the Soil Air 321 

FACTORS affecting THE AMOUNT OF CARBON DIOXIDE IN THE SOIL AIK 

Soil organisms 

Most investigators consider that soil organisms play a large part in the 
production of carbon dioxide in the soil. Pettenkofer (1858, 1871, 1873, 
1875) concluded, as a result of his investigations, that most of the carbon 
dioxide in the soil is due to living organisms. 

Later, E. Wollny (1880b) found that there is only a small production 
of carbon dioxide in an atmosphere of hydrogen gas, while cliloroform 
ahnost completely stops the power of the soil to form carbon dioxide. 
He concluded that carbon dioxide is produced largely by bacteria. 

Further confirmation of this is to be found in the studies of Deh^rain 
and Demoussy (1896), which showed that sterile soil at a temperature of 
22° C. produces only insignificant amounts of carbon dioxide. Stoklasa 
and Ernest (1905), after working with beets, clover, oats, and other plants, 
noted that a bare soil produced, in one hundred and fifty days, more than 
twice the carbon dioxide produced by a crop of wheat on the same area in 
sixty days. They observed also a correlation between the numbers of 
bacteria and the carbon dioxide produced at different depths in the 
soil. Hutchinson (1912) concluded that carbon-dioxide production is a 
reliable measure of bacterial activity. 

Soil conditions 
Where soil conditions are favorable to the action of bacteria, the carbon- 
dioxide content is usually high. For example, Stoklasa (1911) obtained the 
greatest production of this gas in a soil that was well aerated, sHghtly 
alkaUne, and well suppKed with readily available plant nutrients. This 
was found by E. Wollny (1897), Russell and Appleyard (1915), and others, 
to be especially true in the case of soils having readily available organic 
matter. Very small amounts of carbon dioxide were found in the swamp 
rice lands of India by Harrison and Aiyer (1913), showing that unfavorable 
soil conditions are associated with a low content of carbon dioxide. 

Seasonal conditions 
Russell and Appleyard (1915, 1917) emphasized the importance of 
seasonal conditions on the carbon-dioxide content of the soil. In their 
investigations they observed that a rise of temperature is accompanied 



322 H. W. TuEPiN 

by an increase in carbon dioxide. Tlie same fact had been previously 
noted by MoUer (quoted by E. WoUny, 1880 a), by Deherain and Demoussy 
(1896), by Stoklasa and Ernest (1905), and by Leather (1915), and was 
later mentioned by Potter and Snyder (1916). 

Carbon-dioxide production was found by the Rothamsted investigators 
(Russell and Appleyard, 1917) to be correlated ^^dth moisture and rain- 
fall. Previously E. Wollny (1880a) had observed that increasing amounts 
of water up to 9 per cent, in a quartz sand mixed with peat, resuhed in an 
mcrease in the carbon dioxide. Deheram and Demoussy (1896) found that 
there was an optimum water content for carbon-dioxide production in a 
garden soil. Van Suchtelen (1910) found the greatest amount of carbon 
dioxide when the soil with which he worked was 75 per cent saturated 
with water. 

The relationship observed by RusseU and Appleyard (1917) between 
the ramfaU of the preceding week and the carbon-dioxide content of the 
soil, was believed by them to be due largely to the oxygen dissolved in 
the ram water. That this may be true is shown by the earher work of 
E. WoUny (1897), and also by that of Fodor (1875), who showed that 
there is a relationship between the- carbon-dioxide content and the oxygen 
of the soil, mdicatmg that the carbon dioxide is probably produced by 
oxidation processes. 

■ The crop 
The evidence available thus seems to point to bacteria as the chief 
source of soil carbon-dioxide. There are some data, however, which 
show that plants may play a considerable part m the production of this 
gas in the soil. 

Stoklasa and Ernest (1909) and Aberson (1910) noted that the roots of 
plants excrete large amounts of carbon dioxide. That the gas so formed 
IS not msignificant is proved by the fact that field studies conducted 
at Rothamsted by Russell and Appleyard (1917) showed a considerably 
higher content of carbon dioxide in cropped soil than appeared in the 
bare soil, this being especially marked in May, at the trnie of the most 
active growth of the plant, and at the time of ripening. The same condi- 
tion was observed by Bizzell and Lyon (1918) in the case of an oat crop on 
Uunlark clay loam, where the greatest production of carbon dioxide took 
place at about the time of blooming. Potter and Snyder (1916) observed 



The Cahbon Dioxide of the Soil Air 323 

similar results with timothy, but they were unable to decide whether or 

not this increase of carbon dioxide was due to the plant-root excretions 

or to the decay of root particles that had died during the growth of the 

crop. The work of Stoklasa and Ernest (1905) showed that the younger 

the plant is, the greater is the amount of carbon dioxide formed. Kosso- 

witch (1904) noted that mustard grown in quartz sand and nutrient 

solutions produced an increased amount of carbon dioxide up to the 

time of blooming. This was observed also by Barakov (1910) in the 

case of plants growing in lysimeters. 

That different lands of plants produce different amounts of carbon 

dioxide has been shown by Lau (1906), who found that potatoes and 

legumes give off more carbon dioxide than do other crops. Red clover, 

beets {Beta vulgaris), and oats were found by Stoklasa and Ernest (1905) 

to produce more carbon dioxide than other plants, and in the order named. 

Russell and Appleyard (1915), however, could find no difference in the 

carbon-dioxide content of soils on which different species of plants were 

growing. 

Chemical factors 

From the brief survey given, it would seem correct to say that most 
of the carbon dioxide found in the soil is the result of biological activity. 
There is some evidence, however, showing that chemical action may play 
a small part. E. Wollny (1880 b) noted a very slight production of carbon 
dioxide in soil treated with chloroform. The same investigator demon- 
strated later (E. Wollny, 1897) that organic matter in the absence of 
oxygen reduces manganese and iron oxides and forms carbon dioxide. 
Very little carbon-dioxide production in sterihzed soil kept at a 
temperature of 22° C. was observed by Deh^rain and Demoussy (1896). 
They found, however, a very considerable production of carbon dioxide 
in soil heated to 90° C. and above. An oxidizing enzyme in the excretions 
of the root hairs was considered by MoUsch (1888) to be capable of 
producing carbon dioxide from organic substances. It is probable that 
carbon dioxide produced by chemical means forms an extremely small 
part of the total carbon dioxide found in the soil. 

Summary 
In this review of the literature of the subject, certain facts stand out. 
Authorities are agreed that bacteria play an unportant part, probably 



324 H. W. TuRPiN 

the most important part of all the factors concerned, in the production 
of carbon dioxide in the soil. Climatic factors, such as temperature, 
rainfall, and air supply, have a marked effect on the carbon-dioxide content 
of the soil. Crops increase the amount of carbon dioxide in the soil, 
either by direct excretions from the roots or thru the decay of root 
particles from the growing crop. Finally, the nature of the soil itseK 
causes marked differences in the production of carbon dioxide. 

The results reported in this paper confirm some of the above con- 
clusions, but they also show that the influence of the crop has been under- 
emphasized. 

EXPERIMENTAL WORK 

In the author's first experiment, a study was made for two seasons 
(1917 and 1918) in the greenhouse, with soil cropped to oats and with 
uncropped soil. The object was to try to establish some definite relation- 
ship between the carbon dioxide in a cropped soil and that in an uncropped' 
soil, where the crop itself introduced the only variable. Such a relationship 
having been established, it was decided to determine in the second 
experiment whether or not it would hold for a different crop. The third 
experiment was designed to analyze the factors concerned in the production 
of carbon dioxide, and, if possible, to assign to each its respective part. 

EXPERIMENT 1 

The cylinders illustrated in figure 44 were used in the first experiment. 
These cyUnders, eight in number, were made of galvanized iron, coated 
inside with a layer of paint to insure their being air-tight at the joints 
and to prevent rusting. They were 3 feet high by 1 foot in diameter, 
and each had a cone-shaped bottom leading to the cocks on the outside 
as indicated in figure 45. 

The cone-shaped bottom was filled with gravel, above which was placed 
a 12-inch layer of soil from the second foot of the field soil. Above this 
was placed a foot of surface soil. The soil used was Dunkirk clay loam. 
The moisture in the soil was maintained thruout the course of the 
experiment at 30 per cent on the oven-dry basis. The soil was covered 
with a half-inch layer of quartz sand in order to reduce the evaporation, 
the sand being added to the cropped soil immediately after seeding. The 
dry weight of the soil in each of the cans was 94.3 pounds. 



The Carbon Dioxide of the Soil Air 



325 




-' ■ .# 



Fig. 44. c.^ns used ix first experiment 

The four cans at the left contain an oat crop, which is shown at the period of its growth a montii before 
the maximum amount.,of carbon dioxide was found in the air of the cropped soil 




Fig. 45. arrangement of cylinder, sampling flasks , and aspirator 



323 H. W. TuRPiN 

Before seeding, some preliminary studies were made in order to ascertain 
the best method of obtaining the sample of soil air for analysis. It seemed 
impracticable to use any method other than one that could be carried 
out rapidly, since it was planned to run the test for two seasons and to 
take the samples twice each week thruout the year. As a result of the 
preliminary studies, it was found that by aspirating four Hters of air thru 
the soil cans in five minutes, and passing the air thru two graduated 
500-cubic-centimeter Erlenmeyer flasks, samples could be obtained in the 
two flasks which checked with each other, indicating that the air originally 
present in the flasks had been replaced by a representative sample of the 
air in the soil. If more or less than four liters was aspirated thru the 
soil, the amounts of carbon dioxide in the two flasks did not check, indi- 
cating, in the first case, that the original air in the soil had been replaced 
by air from the atmosphere and that some of the latter was passing into 
the flasks, and in the second case that the original air in the flasks had 
not been completely replaced in the flask nearer the aspirator. The 
method of sampUng is shown in figure 45. After the aspiration was 
completed, the cocks on the flasks were closed and the flasks were removed 
to the headhouse, where they were allowed to reach room temperature. 
The excess pressure in the flasks was reUeved by opening one of the cocks 
for a moment. The temperature was noted at this point, as all calculations 
were reduced to per cent by volume of carbon dioxide at standard 
atmospheric conditions, that is, 760 milhmeters pressure and 0° C. 

Excess of standard barium hydroxide was next run into the flasks. 
The volume of the barimn hydroxide added was noted, and .was sub- 
tracted from the total volume of the flask. The cocks were then closed, 
and the flasks were allowed to stand, with occasional vigorous shaking, 
for about thirty minutes, after which the excess barium hydroxide was 
determined by titrating with standard oxalic acid whose equivalent in 
terms of carbon dioxide had been previously determined by titrating 
with standard potassium permanganate solution. 

The method of aspirating air thru the soil has been criticized by Pot- 
ter and Snyder (1916) in a paper describing experiments in which 
they determined the carbon dioxide evolved by drawing, a current of air 
continuously over the soil surface. They maintain that the occasional 
drawing of air thru the soil will result in a temporary decrease in the 
content of carbon dioxide, which, however, will soon be restored by the 



The Carbon Dioxide op the Soil Am 327 

activities of the soil, and tliis accumulation of carbon dioxide will, by the 
mass action law, finally result in a retardation of further production of 
the gas. On the other hand, they maintain that by drawing a current 
of air continuously over the surface of the soil, conditions more nearly 
similar to those obtaining in the field will result. This may be true for 
experiments conducted in a quiet room; but in the greenhouse, where there 
is a circulation of air, there is ample opportunity for diffusion to take 
place from the soil, especially where, as in these experiments, one of the 
lower cocks of the soil can was always left open, so that a sample taken 
at any particular tune should be truly representative of the carbon dioxide 
actually present under normal conditions. 

It has been pointed out by Leather (1915) that usually only about 
25 per cent of the carbon dioxide in the soil is in the gaseous state, 
the remainder being dissolved in water. It is reasonable to suppose that, 
once the soil water is saturated with this gas, any further production of 
carbon dioxide will tend to increase the content in the soil air. Considering 
these facts, then, it will be seen that the method used in these tests will 
not give, and was not intendedto give, absolute amounts of carbon dioxide; 
but it nevertheless should yield reliable relative values. 

On April 2, 1917, the soil, which is a heavy clay loam rich in silt and 

having a lime requirement of about 3000 pounds to the acre (Veitch), 

was brought up to 30 per cent moisture content on the oven-dry basis. 

Four of the cans were seeded to White Russian oats. A half-inch layer 

of quartz sand was then spread over the surface of the soil in the eight cans. 

From April 12 to September 28 the samples were taken twice a week. 

From September 29 the sampHng was done approxunately once in two 

weeks imtil February 7, 1918, after which date the samples were again 

taken twice a week. The second crop of oats was planted on January 9. 

Some fifty seeds were usually sown, and the plants were thinned out in 

the course of two weeks to fifteen in each can. In the season of 1917, one 

plant became infected with smut, and on June 13 this plant was removed, 

together with one plant from each of the other cans. To maintain the 

moisture content of the cropped cans at 30 per cent (oven-dry basis) 

frequent waterings were necessary, especially at the time of most vigorous 

growth. At that period the cropped cans were irrigated once a day. 

The amount of water added was recorded in order to see whether or not 

there was any relationship between the transpiration and the carbon- 



328 H. W. TuBPiN 

dioxide production in the cropped soil. Since only about a quarter of 
a pound of water was lost in a week from the uncropped soil, tap water 
was used m all cases, as the small loss by evaporation could not possibly 
mtroduce a disturbing element in the form of an accumulation of soluble 
salts in the soil. 

Results 

On each date of sampling, the samples were taken in duplicate from 
each of the eight cans. Thus eight samples were obtained from the 
cropped soil and eight from the bare soil. Smce all of the four cropped 
cans were treated in identically the same manner, the data for the duphcate 
samples from the cropped cans were averaged. This was done also in 
the case of the bare soil. 

It seemed fair to average the data obtained from the cans in each set 
because m all cases the differences were small. This is shown by the very 
small probable error. The data for the oat crops of 1917 and 1918 are 
given m tables 1 and 2 (appcmdix, pages 353 to 356), each figure for carbon 
dioxide m these two tables being the average of eight determinations. 
Ihese summarized results are represented diagrammatically in figures 
45 and 47. 

Effect of crop 

The content of carbon dioxide at the beginning of the experiment was 
U..b per cent by volmne for both cropped and uncropped soil. From that 
oime on, as may be seen from figiures 46 and 47, the amount of carbon 
dioxide in the uncropped soil in no case reached that in the cropped soil — 
not even after the removal of the crop. The latter point may perhaps be 
explained by the fact that since the roots of the crop were not removed 
trom the soU at harvesting, they somewhat increased the available supply 
of organic matter. The results reported here are directly opposite to 
those of Bizzell and Lyon (1918), who worked with the same Dunkii-k 
clay loam under field conditions and found that subsequent to the removal 
ot the oat crop a marked decrease in carbon dioxide below that in the 
uncropped soil took place. This was not found to be the case, however 
with the Volusia silt loam used by these investigators 

A study of figure 46 shows that in the season of 1917 there was a marked 
mci-ease m the carbon dioxide in the cropped soil from the beginning 
of May, amonth after seeding, until the maximimi, 2 per cent, was reached 



The" Carbon Dioxide of the Soil Aih 



329 




April May Juuo July AfS- Sept. Oct. I 

Fig. 46. caebon dioxide in air from Dunkirk clay loam cropped to 
from the same soil left bare, w17 

Fer cent 
of CO2 



ov. Dee. 

OATS AND 



Oaf crop - 
A/o crop ■ 



y9/3 




Fig. 



Feb. March April May June July 

47. aARBON DIOXIDE IN AIR FROM DUNKIRK CLAY LOAM CROPPED TO 
FROM THE SAME SOIL LEFT BARE, 1918 



Aug. 
OATS AND 



330 H. W. TuEPiN 

in the first week of June, at the time when the plants were starting to 
head. Thereafter the general tendency of the curve for the cropped soil 
was toward a decrease, altho it was not until the middle of July, two 
weeks previous to harvesting, that this decrease was very marked. It was 
pointed out by Russell and Appleyard (1917) that in their experiments 
a large increase in carbon dioxide was observed in the cropped soil at 
the time of ripening; but, as can be seen from figures 46 and 47, in neither 
1917 nor 1918 was any such increase noted in this work. If anything, 
the ripening was accompanied by a marked decrease in carbon dioxide' 
as is shown especially for the season of 1918 (fig. 47). Subsequent to 
the removal of the crop, the carbon dioxide in the cropped soil con- 
tinued to decrease, but never to a point below or equal to that in the 
uncropped soil. 

It is interesting to note that in 1917, fluctuations in the content of carbon 
dioxide in the uncropped soil were accompanied by similar variations in 
the cropped soil during the early part of the season and subsequent to 
harvestmg. This was not true during the period of active growth of the 
plant, which would seem to indicate that at that time the life activity 
of the crop itself, rather than that of the soil organisms, is playing the 
dominant part in controUing the production of carbon dioxide. 

What has been said for the season of 1917 holds for 1918 also. During 
the latter season, however, there was a much more marked increase in 
the carbon dioxide of the cropped soil. By the 1 1th of April, three months 
after seeding, more than 3 per cent of carbon dioxide was found, as com- 
pared with a Httle less than 0.2 per cent in the uncropped soU This 
occurred four weeks previous to heading. Thereafter the content of 
carbon dioxide in the cropped soil increased to the maximum of 3 34 
per cent, which occurred a week before heading and coincident with 
the tune of rapid elongation of the cuhns. Following the maximum there 
was a steady dechne. The decrease was especiaUy marked dming early 
June, when the upper glumes were beginning to turn yellow and the 
plants were starting to mature. In figure 44 (page 325) the plants are 
shown a month before the period of maximum carbon-dioxide production. 
Since the maximum of 3.34 per cent of carbon dioxide found in the soil 
was about the same as that noted by BizzeU and Lyon (1918) in 'their 
studies with Dunkirk clay loam cropped to oats, it is evident that the 
decrease m the production of carbon dioxide in the cropped soil below 



The Carbon Dioxide of the Soil Air 331 

that in the uncropped soil after the removal of the crop, reported by 
these investigators, may not be due to interference with bacterial activities, 
since in the work reported in the present paper no such action on the soil 
organisms, as evidenced by a decrease in carbon-dioxide production, was 
observed. It may be possible that the decrease noted by BizzeU and 
Lyon was due to some other eifect of the crop, such as, for example, the 
reduction of the soil moisture. It has been pointed out in the review 
of the literature of the subject that some investigators have noted a 
decrease in carbon dioxide where the moisture was reduced below a certain 
optimiun amount. On referring to figure 46 it will be seen that early in 
July, 1917, the carbon dioxide in the cropped soil showed a marked 
decrease. Tliis was due to the drying-out of the soil when, thru an over- 
sight, it was not watered for two days. 

It has been pointed out that the carbon dioxide in the cropped soil 
was somewhat higher (about 30 per cent) in 1918 than it was in 1917. 
The results for the two seasons are not strictly comparable, because in 
1917 the crop was sown in April whereas in 1918 the seeding was made 
in January. Also, in 1917 the number of plants was reduced to fourteen 
in each pot, while in 1918 there were fifteen. However, the total dry 
weight of the mature crop from the four cans in 1917 was 494.5 grams, 
as against 416 grams in 1918. 

Carbon-dioxide and water relationships 

As has already been stated, a record was kept of the amount of water 
added to the cropped cans in order to maintain them at a moisture content 
of 30 per cent (oven-dry basis). The sand mulch on the soil, as has been 
pointed out also, was so effective that the loss ia moisture on the cropped 
cans could be regarded as due entirely to transpnation. 

The total amount of water lost on the cropped cans each week was 
determined in 1917 and 1918 for a period of ten weeks during which the 
crop was making the most active growth. These amounts, together with 
the average weekly content of carbon dioxide in the cropped and the 
uncropped soil, are indicated in tables 3 and 4 (appendix, pages 357 to 
358) , coliunns A, C, and E. The difference between the carbon dioxide in 
the cropped and that in the uncropped soil is given in column F of the 
same tables. The carbon dioxide produced to each poimd of water used 
is shown in colunms G and H. The figiires in colimm G were obtained 



332 



H. W. TtmpiN 



by dividing the weekly carbon-dioxide percentage in the cropped soil after 
the carbon dioxide in the bare soil had been subtracted, by the weeldy loss 
of water in pounds. The figures in column H, however, were obtained 
by dividing the weekly carbon-dioxide percentage in the cropped soil by 
the weekly loss of water without first subtracting the carbon dioxide in 
the bare soil from that in the cropped soil. 

The relationship between the carbon dioxide produced in the cropped 
soil (from which has been subtracted the carbon dioxide in the bare soil), 
and the water transpired by the crop, is shown graphically in figures 
48 and 49. There seems to be a relationship between the amount of 
water transpired and the carbon dioxide produced by plants, as is indicated 



Per cent 
ofCOj 



Pounds 
of water 



2.6- 


y\^ 


2.5- 


/ \ 


2.4- 


/ N. 


2.3l 


/ N. 


2.2- 


/ ^^ 


2.1- 


/ ■ \^ 


2.0- 


^,^.-^ \ 


1.9- 


y^'""^ \ 


1.8- 


y^ \ 


1.7- 


/ 


1.6- 


J^ 


1.5- 


^^ 


1.4- 


^^ 


1.3- 
1.2- 


/^ ..... 


1.1- 
1.0- 


r~~~-~^ y"' ■•.. .,•••■■■' 


0.9- 


/ -■ '■-.•■' 


0.8- 


/ 


0.7- 


/••''"' 


0.6- 


/ .•''' 


0.5- 




0.4- 
0.3- 
0.2- 




0.1- 





40 



30 



May June .)uiy 

Fig. 48. relation between watek tkanspibed and carbon dioxide produced 

BY AN oat crop FOR THE TEN WEEKS DURING WHICH ITS GROWTH WAS MOST VIG- 
OROUS, 1917 



by tables 3 and 4 and by figures 48 and 49. The illustrations show that 
the curves for the water transpired each week, and for the carbon dioxide 
obtained by subtracting the carbon dioxide in the bare soil from that 
in the cropped soil, follow each other closely. The data given in the 



The Carbon Dioxide of the Soil Air 



333 



tables and plotted in the curves are for the period of ten weeks during 
which the plants were growing most actively. Before and after this 
period no relationship was found to exist between the amount of water 
transpired and the carbon dioxide produced by the plants. 



Ter cent 
ofCOj 



of v.iur 




Fig. 49. relation between water transpired and carbon dioxide produced 

BT AN oat crop FOR THE TEN WEEKS DURING WHICH ITS GROWTH WAS MOST VIG- 
OROUS, 191S 

It is seen in columns G and H of tables 3 and 4 that the percentage of 
carbon dioxide produced to each pound of water transpired, approaches 
a constant much more nearly when the carbon dioxide in the uncropped 
soil is subtracted from that in the cropped soil. The smaller coefficients 
of variability of 22.5 d= 3.74 as compared with 37.4 ± 5.65 in 1917, and 
15.1 ± 2.32 as against 19.17 ± 3.12 m 1918, bring out this fact fairly 
clearly. If it is assumed that the amount of carbon dioxide produced 
and the amount of water transpu-ed are indications of hfe activity, then 
the relationships found between the carbon dioxide in the soil, and the 
water transpired, would hold only when the carbon dioxide is produced 



334 H- W. TuRPiN 

by the crop alone. When the carbon dioxide in the uncropped soil was 
subtracted from the carbon dioxide found in the cropped soil, and this 
figure was divided by the amount of water transpired, there resulted 
approximately a constant of 0.024 ± .0012 (column G) with a coefficient 
of variability of 22.5 ± 3.74 for 1917, and a constant of 0.043 ± .0014 
with a coefficient of variability of 15.1 ± 2.32 for 1918. When the carbon 
dioxide in the uncropped soil, which may be attributed to bacterial activity, 
was not subtracted (column H), there resulted a constant of 0.042 ± .0031 
with a coefficient of variabihty of 37.4 ± 5.65 for 1917, and a constant 
of 0.053 ± .0022 with a coefficient of variabihty of 19.17 ± 3.12 for 1918. 

This shows that the constants in the latter cases are not nearly so 
dependable as those in the former, indicating that the carbon dioxide 
produced by the crop is probably the difference between the carbon 
dioxide in the cropped soil and that in the bare soil. That the values 
obtained are not perfect constants can hardly be wondered at when it 
is recalled that the carbon dioxide as determined was not absolute, but 
relative. 

In this connection it may be pointed out that there seems to be some 
groimd for concluding that there is a relationship between the water 
transpired by the plant and the carbon-dioxide content of the soil. 

While it is not disputed that the mechanism by which the water is 
actually lost from the leaves of the plant is purely physical and not at 
all associated with vital plant activity, yet the process by which the water 
is brought into the leaves and into a condition to be transpired may weU 
be considered as being associated with the life activities of the plant. 
Many investigators have maintained that there is a distinct relationship 
between the life activities of plants and the water transpired. For example, 
as early as 1849 Lawes (1850) considered that the comparative rate of 
transpiration of water to some extent indicated the relative activity of 
the processes of the plant. He drew these conclusions from studies with 
wheat, barley, beans, peas, and clover, in which he compared the amount 
of ash and dry matter obtained from the plants with the water given 
off by them. He found that the larger the amoxmt of dry matter, the 
greater was the quantity of water transpired. These views are supported 
by the investigations of Sorauer (1878, 1880), but the work of Walter 
Wollnjr (1898) leads to an opposite conclusion. In 1905 Livingston 
(1905) worked with wheat seedlings and concluded that total transpiration 
is as good a criterion for comparing the relative growth of plants in 



The Carbon Dioxide of the Soil Am 335 

different media as is the weight of the plant itself. Hasselbring (1914), 
however, after growing plants under cheesecloth and in the open, stated 
that the mere passage of water thru the plant had no influence on the 
assimilatory activity of the plant, provided the water supply did not 
fall below a certain minimum required to maintain turgor of the cells. 
Stoklasa and Ernest (1909) determined the carbon dioxide given off by 
different plants grown in various nutrient solutions, and obtained the 
results presented in table 5 (appendix, page 358). These figures show 
that there is a definite relationship between the total dry weight of 
different crops and the carbon dioxide produced. The average of 0.037 
milligram of carbon dioxide to each milhgram of dry matter seems to be 
independent of the kind of plant used in the test. 

From the short review given, it would seem that the evidence is in 
favor of the assumption that transpiration is related to life activity of 
plants as indicated by a relationship between the dry matter and the 
water transpired. The work of Stoklasa and Ernest (1909) would point 
to a correlation between the carbon dioxide produced and the dry matter 
in the plant. 

Effect of temperature and atmospheric pressure 

The relationship between the temperature and the atmospheric pressure 
at the time of samphng, and the carbon dioxide in the air of the uncropped 
soil, is shown graphically in figures 50 and 51 for the seasons of 1917 and 
1918, respectively. The temperature at each time of sampling was found 
to be approximately representative of the temperature for the preceding 
twelve-hours period. The pressure also would probably represent the 
average of several hours preceding the samphng. 

On the whole the figures bring out only a few striking facts. High 
temperatures were usually accompanied by a high percentage of carbon 
dioxide, while high atmospheric pressures were usually associated with 
a low carbon-dioxide content. High pressures along with high tem- 
peratures gave fairly high contents of carbon dioxide, indicating that 
temperature has a more marked effect than pressure. When the temper- 
ature and the pressure were medium there appeared to be no relationship 
with the carbon-dioxide content. Very low temperatures were always 
accompanied by a low content of carbon dioxide; but, while a very low 
pressure did not necessarily mean a high carbon-dioxide content, it was 
usually associated with such a condition. 



336 



li. W. TuRPiw 



Per cent 
of 00= 



2 2 

2,0 

LS 

1 6 

1.4 

1.2 

1.0 

0-8 

0.6 

OAi 

0.2 






^f/r7c?s/^/yffr/c /:?rff^:y Si/re — 1 



;i I 






J ^ I 



April 



May 



June 



.Tu!y 



j_i_y_ 



Temp. 

fC.) 


Mm. pr. 
(inches) 


36° 
•34° 


29.6 


•32° 
•30° 


29.4 


• 28° 
■26° 


29.2 


24° 
22° 


23.0 


20° 
18° 


28.8 


16° 
14° 


28.6 



Fig. 50. relation between the tempekatukb of tse soil at ths time of "sampling, 
the atmospheric pressure, and the carbon dioxide in the air op the uncropped 

SOIL, 1917 



Per cent" 
ofCC: 



1.1 
1.0 
0.9- 
0,8- 
0.7- 
0.6 
0,5 
0.4 
0.3 
0.2 
0.1 



_ Temp Atm. pr. 
"(C.) (inches) 



C'P/-£'C3^ cf/ox/o'tr 

7jvT?/:>e/r^/t//yT 




Fig. 51. relation between the temperature of the soil at the time of sampling, 
the atmospheric pbessube, and the carbon dioxide in the aib of the uncbopped 

SOIL, 1918 



The Carbon Dioxide of the Soil Air 337 

Summary oj experiment 1 

The results of the first experiment may be siimmarized as follows: 

1. Soils cropped to oats always contained a greater amount of carbon 
dioxide than did the corresponding bare soils. 

2. The crop had a residual effect, increasing the carbon-dioxide content 
above that in the uncropped soil. 

3. The difference between the amount of carbon dioxide in the cropped 
soil and that in the uncropped soil at the period of most active crop growth, 
divided by the amount of water transpired by the crop, gave an apparent 
constant which varied with the season. 

4. The fact just stated may indicate that the difference between the 
amount of carbon dioxide produced in the cropped soil and that in the 
uncropped soil represented the amount produced by the crop. 

5. It is thus evident that the carbon dioxide from plants and from soil 
organisms accumulated independently. 

6. Fluctuations in the amount of carbon dioxide in the uncropped soil 
were due largely to temperature and pressure variations. High pressures 
produced low contents of carbon dioxide, while high temperatures caused 
high production of carbon dioxide, and vice versa. 

EXPERIMENT 2 

The object of the second experiment was to determine the influence 
of some crop other than oats on the production of carbon dioxide. The 
crop used in this case was common millet {Setaria italica). 

Immediately after the harvesting of the 1918 oat crop, millet was planted 
on the same soil and in the same cyHnders as were used in experiment 1. 
For experiment 2 the sm-face layer of Sand was entirely removed from 
the soil, which was then thoroly stirred to a depth of about three inches. 
The millet was seeded on four of the soils, of which two had previously 
been in oats and two had been bare. The object in using these two 
different sets was to try to produce some differences in the two crops 
of millet. It was thought that possibly the millet growing on the soil 
which had been previously cropped twice to oats, might not grow well, 
and in such a case a comparison could be made between a good and a 
poor crop of millet. 



338 



H. W. TURPIN 




Fig. 52. millet crops six weeks after seeding, on the two soils having high and 
LOW initial contents of carbon dioxide, respectively 

Close view, showing details 



The crop was planted on July 1. Within three weeks after planting, 
the crop on each can had been thinned out until forty plants remained. 
The number of plants to a pot was reduced in the next week to thirty. 
At first the samples were taken twice a week, as in the case of experi- 
ment 1 ; but later — from the middle of August — when the crop was 
making very rapid growth, samples were taken every day. Toward the 
end of August the samples were taken every other day. As in experi- 
ment 1, the moisture in the soil was maintained at 30 per cent (oven- 
dry basis). 

At the time when the experiment was discontinued, the plants were 
completely headed. In the case of series 1 (soil previously cropped to 
oats) the plants were beginning to show signs of maturing; in series 2 
(soil previously bare), however, the grain was still between the milk 
stage and the dough stage. 

The crops on series 1 and 2 were identical in all details until a few 
days after heading. This may be seen in figures 52 to 55. Thereafter 
the plants in series 2 maintained their dark green color, while those in 



The Cakbon Dioxide of the Soil Air 



339 




Fig. 53. millet chops six weeks after seeding, on the two soils having high and 
LOW initial contents of carbon dioxide, respectively 
Same as figure 52, but showing cylinders 

series 1 gradually became light green, until finally, when the experiment 
was stopped in September, the latter were beginning to mature while 
those in series 2 had not yet begun to show signs of ripening. 



Results 

The results of experiment 2 are summarized in table 6 (appendix, 
page 359), in which each figure represents the average of two duplicate 
samplings from each of two pots, an average of four samplings in all. 



340 



H. W. TUEPIN 




■Fig. 54. Millet crops seven and one-half v>fEEK3 aftjsr seeding, on the two soils 

HAVING HIGH AND LOW INITIAL CONTENTS OF CARBON DIOXIDE, RESPECTIVELY 
Close view, showing details 



These data arc presented diagrammatically in figures 50, 57, and 58, the 
first two representing the data for series 1 and 2, respectively, and the 
third giving these two sets of curves on one sheet. 

It will be noticed that the carbon dioxide in the cropped soils and 
that in the uncropped soils remained the same for the first four weeks 
after seeding. Thereafter the curves, for the cropped soils separated 
fairly rapidly from those for the bare soils. In this respect there is no 
difference between the oats and the millet. It will be observed, however, 
that whereas the two oat crops attained their point of maximum carbon- 
dioxide production shortly before heading, the miUet crops both gave 
the most carbon dioxide just ten days after heading. In order to bring 
out this point more clearly, curves showing the relationship between the 
amount of carbon dioxide in the oaf soil (1917) and that. in the millet 
soil (series 2) have been plotted together in figui-e 59, in such a manner 
that the carbon dioxide produced at the period of heading of each of 
the two crops is on the same ordinate, with the data for a few weeks 



The Cabbon Dioxide of the Soil Aih 



241 




Fig. 55. millet crops seven and one-half weeks after seeding, on the two soils 
having high and low initial contents of carbon dioxide, respectively 

Same as figure 6i. but showing cylinders 

before and a few weeks after the heading period plotted to the left and 
to the right of this point, respectively. 

Since the experiment was discontinued before the millet crops matured, 
it is not possible to say whether or not the curve for the later period of 



342 



H. W. TuKPm 



Per cent 
ofCOs 



4.S 
4 fi- 






/////£•/ 




4.4- 




A/oCro/^ 


o^ /h/hfy CO -so// 


4.2- 






- 


^ 


4.0- 
3.8- 








|- 


a.fi- 








&s 


3.4- 
3.2- 




1 




^ 


3.0- 




t 
f 




X 


2.8- 
2.6- 
2.4- 


§- 


"1 > 


/ \ 


2.2- 
2.0- 


^ 


/-^ 


\J 


V 


1 S- 


^ ^ 






^ 


1.6- 


I /■■•• 


' ' "' \ / 






1.4- 


^ / 


•V / / '" 






1.2- 


^ / 


' ^"*'*'v/ * 






1.0- 
0.8- 


L/ 


'•. / 


••.._ 


.-■■■••••. 


0.6 




• 






0.4- 










0.2- 











July August tiept. 

ElG. 56. CARBON DIOXIDE IN AIR FROM DUNKIRK CLAY LOAM PHE-V10USLT CROPPED 
TWICE TO OATS, CROPPED TO MILLET, AND FROM THE SAME SOIL LEFT BARE, 1918 

Per cent 
of CO2 



4.6n 














4.4-1 














-( '' 








Af/'/M/nrp 




4.0- 








A/a 


cz-o/? 


o/y /cjf^CO so/V 


3.8- 














3.6- 












1 


3.4- 












3.2^ 












zM 












2.8- 












$ 


2.6- 






> 






/\ 


2.4- 






^^ 






/\ 


2.2- 


^ 




1 


\ 


1 


/ ^---^ 


2.0- 
1.8- 


1 


1.6- 
1.4- 


-r 




A^ 


i 


y 




1.2- 


^ 




/ ^ 








1.0- 


8 












0,8- 


^ 


^iT^'*''*'^" ^'^ — -J 










0.6- 




*., 


•-. 








0.4- 


*'-..•• 




'• 


•••..•• 




0.2- 


















)\. 






-^ 


n 



July 



August 



Sept. 



Fig. 57. 



CARBON DIOXIDE IN AIK FROM DUNKIRK CLAY LOAM NOT PBE-VIOUSLT CROPPED, 
CEOPPED TO MILLET, AND FROM THE SAME SOIL LEFT BABE, 1918 



The Carbon Dioxide of the Soil Air 



343 



Per cent 
of CO3 




h/^/7 CO ^o// 



/o^ CO so// 



A/oprqp or? 
/7/hr/7 CO^^o// 

-./ 






zr 



July 



zxz 



'^r 



. August 

Fig. 58. relation between the amounts of carbon dioxide in air from cropped 
and from uncropped dunkirk clat loam having high and low initial contents 
of carbon dioxide, respectively 




Oaf crop, /9/r ■ 



4321 1234 

Weeks before heading Weeks after heading 

Fig. 59. relation between the amounts of carbon dioxide in air from dun- 
kirk CLAY loam cropped TO OATS AND MILLET, RESPECTIVELY, BEFORE AND AFTER 
THE CROPS HEADED 



344 H. W. TxjBPiN 

growth of the millet would resemble in genera] that for the oat crops. 
The general tendency of the cm-ve after August 25 was to fall as the plants 
advanced toward maturity, as in the case of the oat crops. It will be 
noticed from figure 59 that the actual amount of carbon dioxide produced 
on the soil cropped to mUlet was much the same as that produced on the 
oat son. The maxima for the two pat crops of 1917 and 1918 were, 
respectively, 2.031 per cent and 3.343 per cent, while the corresponding 
figures for the millet crops in series 1 and 2 were 3.345 per cent and 2.715 
per cent. It must be remembered, however, that there were but fifteen 
oat plants as compared with thirty millet plants; so that it may be con- 
cluded that an individual oat plant causes the production of about twice 
as much carbon dioxide as is produced by a miUet plant. 

Summary of experiment 2 
From the results of the second experiment it may be concluded that 
a soil cropped to millet causes about the same fluctuations in carbon- 
dioxide production as are found in a soil growing an oat crop. In general, 
however, the oat crop gives the greatest production of carbon dioxide 
previous to headmg, while the millet has its most marked effect a week 
or two after heading. It would seem also that an individual millet plant 
causes the production of approximately haK as much carbon dioxide 
as an mdividual oat plant. From the close agreement between the two 
curves shown in figures 56, 57, and 58, for series 1 and 2, it may be assumed 
that in spite of shght differences in the previous treatment of the soil 
the excess carbon dioxide due to the crop was fairly shnilar where the 
crops growing showed no apparent differences m vigor. This is indicated 
also m figures 62 to 55, which show the two crops at an early and at 
a later stage of growth, the crop on the soil previously cropped twice to 
oats being designated as a high-carbon-dioxide crop and that on the soil 
that was previously bare being called a low-carbon-dioxide crop. 

EXPERIMENT 3 

As is pointed out in the review of Uterature, it is not clear whether or 
not the increased amount of carbon dioxide observed in a cropped soil 
is due to the excretion of carbon dioxide by plant roots (plant activity) 
or to the decay of root particles from the growing crop (bacterial activity). 
Data obtained in experiment 3 seem to throwa httle fight on tins question. 
In this experiment, cans 1, 2, 3, and 4, which had previously grown two 



The Caebon Dioxide of the Soil Air 345 

crops of oats, had a considerably higher content of carbon dioxide, even 
after the removal of the crop and especially for about two months after 
harvest, than did cans 5, 6, 7, and 8, which remained imcropped for the 
two seasons. 

After the oat crop from cans 1, 2, 3, and 4 was harvested, on July 1, 
1918, cans 2 and 3, and the uncropped cans 6 and 8, were seeded to millet. 
Cans 1, 2, 3, and 4 are here designated as the high-carbon-dioxide series, 
while cans 5, 6, 7, and 8 are called the low-carbon-dioxide series. Thus, 
in the high-carbon-dioxide series, cans 1 and 4 were bare and cans 2 and 3 
were cropped to millet; in the low-carbon-dioxide series, cans 5 and 7 
were bare and cans 6 and 8 were cropped. All these cans were sampled 
in the usual way for carbon dioxide, and the data obtained are given 
in table 7 (appendix, page 360). The samples were taken twice a week 
at first, and later they were taken daily. The moisture in the soil was 
maintained at or near 30 per cent (oven-dry basis). 

Within a month of seeding, the crop was thinned to thirty plants to 
a can; so that at the time when the effect of the plants on the carbon 
dioxide became noticeable (a month after seeding), the number of plants 
was the same for all cans. 

Results 

In table 7 it is shown that the differences between the percentages of car- 
bon dioxide in the cropped soil and those in the uncropped soil in the high- 
carbon-dioxide series, were approximately the same as the corresponding 
differences in the low-carbon-dioxide series. .In table 8 (appendix, page 361) 
it is seen that the majority of the differences in carbon-dioxide production 
by the crop in the two series (as determined by the difference between the 
amount of carbon dioxide produced by the cropped soil and that produced 
by the uncropped soil) was well witliin the hmits of the experimental error. 
It seems, therefore, that the crops produced carbon dioxide quite independ- 
ently, and that this production was not affected by the amount of carbon 
dioxide in the soil, at least not within the limits set by this experiment. 
How closely the difference between the curves for the cropped soUs cor- 
responded with those for the bare soils is shown in figure 58 (page 343). 

The relationship between the temperature of the soil at the time of 
sampling, and the carbon dioxide in the bare soil and also that due to the 
crop on the Tow-carbon-dioxide series (determined by the difference as 



346 



H. W. TURPIN 



explained above), is shown in table 9 (appendix, page 362) and in figure 60. 
It will be noticed that increases in temperature were more frequently 
accompanied by rises in carbon dioxide in the bare soil (indicating a 
relationship between bacterial activity and carbon-dioxide production), 
than by rises in the carbon dioxide produced by the crop. In the latter 




Cc7rhc!rr c/zox/C^S /"/-c/r? rr?///^/- crop — 




Temp. 
fC.) 
36° 

35° 

34° 

33° 

32° 

31° 

30° 
-29° 
-28° 
-27° 

26° 

25° 

24° 

23° 

22° 

21° 

20° 



1 



12 



15 



19 



26 



August 

Fig. 60. eelation between the carbon dioxide produced bt a millet crop, 
the carbon dioxide in a bare soil, and the temperature op the soil at the 
time of sampling, 191s 

case no such close relationship appeared, but the carbon dioxide increased 
gradually as the age of the plant advanced until the point of maximum 
carbon-dioxide production, after which there was a decline. This increase 
in carbon dioxide seems to have kept pace with the rate of growth of the 
plants. At the time when the plants ceased to grow actively (some time 
after heading), the carbon-dioxide production also fell off. If the excess 



The Carbon Dioxide op the Soil Air 347 

carbon dioxide in the cropped soil is due to the decomposition by bac- 
teria of root particles tin-own off from the growmg crop, then one would 
expect to find that those factors which produce fluctuations in the carbon 
dioxide in the bare soil would produce corresponding, but more magni- 
fied, fluctuations in the cropped soil. But, as is pointed out above, a 
factor such as temperature did not produce corresponding changes in the 
two soils. 

Again, if the decomposition of root particles from the growing crop 
gave rise to the increase of carbon dioxide in the cropped soil, it is reason- 
able to suppose that there would be a much larger increase in carbon 
dioxide at a time when the roots were beginning to die off rapidly, that is, 
toward the ripening period. Such, however, was not the case. 

Summary of experiment S 

It is probable, therefore, that the larger part of the excess carbon dioxide 
produced in a cropped soil is due to respu-atory activities of the plant 
roots, and that the amount resulting from the decay of root particles 
from the growing crop is small — altho after the crop has matured, any 
excess of carbon dioxide found is undoubtedly due to the decay of the 
mass of roots left in the soil. This excess, however, is very small when 
compared with the very large amounts of carbon dioxide found in the 
cropped soil at the time of heading, for example. 

In support of the conclusion that the larger production of carbon dioxide 
in the cropped soil is due to respiratory activities of the plant roots, the 
data presented in experiment 1 show that there seems to be a correlation 
between the. water requirements of the plant, and the amount of carbon 
dioxide produced. 

GENERAL SOIIV'IAEY 

The results of the work reported in tliis paper with regard to the effect 
of crop and other factors on the production of carbon dioxide in a Dunkirk 
clay loam maintained at a constant moisture content of 30 per cent (oven- 
dry basis), may be sununed up as follows: 

1. An oat crop increased the production of carbon dioxide in the soil. 
This increase became marked after the first month from the time of 
seeding, and increased to a maximum just previous to or after the plants 
headed, after which there was a gradual decline. 



348 H. W. TuRPiN 

2. Millet produced about the same increase in carbon dioxide as did 
oats, but the production of carbon dioxide by each millet plant was 
approximately half as much as the production by each oat plant. The 
most marked rise in the carbon-dioxide content of the soil occiured at 
a later period of growth in the case of the millet than in the ease of the 
oats. 

3. The cropped soil, after the crop was harvested, maintained a higher 
carbon-dioxide content than was found in the bare soil. This was due 
probably to the decomposition of plant roots left in the soil. 

4. It would seem that increased plant activity (growth) is accompanied 
by increased carbon-dioxide production. This theory is supported by 
the fact that a relationship was shown between the carbon dioxide pro- 
duced presumably by the crop, and the water transpired. 

5. Fluctuations in the content of carbon dioxide in the bare soil were 
accompanied by sLmUar fluctuations in the cropped soil only after the 
removal of the crop and before the crop had made much growth. 

6. There appeared to be httle relationship between the temperature of 
the soil at the time of samphng, and the carbon dioxide in the cropped 
soil or that assumed to be produced by the crop (determined by sub- 
tracting the carbon dioxide in the bare soil from that in the cropped soil). 

7. In the bare soil the carbon dioxide was usually high dm-ing warm 
weather and low when the temperature decreased. 

8. Very low atmospheric pressures were usually accompanied by an 
increase in the content of carbon dioxide in the bare soil. 

9. The carbon dioxide produced presumably by the plant was about 
the same in soils having a high initial carbon-dioxide content as in those 
low in carbon dioxide, indicating the probabihty that plants and soil 
organisms act independently in producing carbon dioxide. 

10. It is concluded from this work that the plant itself, and soil 
organisms, produce most of the carbon dioxide in the soil; that the plant 
often produces at the period of its most active growth many times as 
much- carbon dioxide as is produced by soil organisms; and that the 
excess carbon dioxide in the soil growing a crop is due to respiratory 
activity of the plants rather than to the decay of root particles from 
the crop growing on the soil at the time of analysis. 



The Carbon Dioxide of the Soil Air 349 



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Aberson, J. H. Ein Beitrag zur Kenntnis der Natur der Wurzelausschei- 
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Barakov, p. The carbon dioxid content of soils during different stages 
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BizzELL, J. A. , AND Lyon, T. L. The effect of certain factors on the carbon- 
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Deherain, P.-P., and Demoussy, E. Sur I'oxydation de la matiere 
organique du sol. Ann. agron. 22 : 305-337. 1896. 

FoDOR, J. V. Der Kohlensauregehalt der Bodengase. Vrtljschr. offentl. 
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Harrison, W. H., and Aiyer, P. A. Subramania. The gases of swamp 
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Hasselbeing, Heinrich. The relation between the transpiration stream 
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Hutchinson, C. M. Report of the Imperial Agricultural Bacteriologist. 
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KossowiTCH, P. [Russian title.] The quantitative determination of 
cai-bon dioxide produced by the roots of plants during the period of 
their development. Zhur. opuitn. agron. 5:482-493. {Abstracted by 
J. Davidson.) 1904. 

Lau, E. Beitrage zur Kenntnis der Zusammensetzung der im Acker- 
boden befindhchen Luft. Inaug. Diss., Rostock. 1906. 

La WES, J. B. Experimental investigation into the amount of water 
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Leather, J. Walter. Soil gases. India Dept. Agr. Memoirs, Chem. 
ser. 4:85-134. 1915. 

Livingston, Burton Edward. Relation of transpiration to growth in 
wheat. Bot. gaz. 40:178-195. 1905. 

MoLiscH, Hans, tjber Wurzelausscheidungen und deren Einwirkung 
auf organische Substanzen. K. Akad. Wiss. [yienna], Math.-Naturw. 
CI. Sitzber. 96(1887) : 84-109. 1888. 



350 H. W. TuEPiN 

Neller, J. R. Studies on the correlation between the production of 

carbon dioxide and tire accumulation of ammonia by soil organisms. 

Soil sci. 5:225-241. 1918. 
Pettenkofer, M. Volumetric estimation of atmospheric carbonic acid. 

Chem. Soc. [London]. Quart, journ. lo: 292-297. 1858. 
Ueber den Kohlensauregehalt der Grundluft im Geroll- 

boden von Munchen in verscliiedenen Tiefen und zu verschiedenen 

Zeiten. Ztschr. Biol. 7:395-117. 1871. 

Same. Ztschr. Biol. 9:250-257. 1873. 

Ueber den Kohlensauregehalt der Luft in der libyschen 



Wiiste iiber imd unter der Bodenoberflache. Ztschr. Biol, ii: 381-391. 

1875. 
Pfeiffee, Th., and Blanck, E. Die Saureausscheidung der Wm-zeln 

und die LosUchkeit der Bodennahrstoffe in kohlensaurehaltigem Wasser. 

Landw. Vers. Stat. 77:217-268. 1912. 
Plummer, J. K. Some effects of oxygen and carbon dioxide on nitrifica- 
tion and animonification in soils. Cornell Univ. Agr. Exp. Sta. Bui. 

384:301-330. 1916. 
Potter, R. S., and Snyder, R. S. Carbon dioxide production in soils 

and carbon and nitrogen changes in soils variously treated. Iowa Agr. 

Exp. Sta. Research bul. 39:249-309. 1916. 
Russell, E. J. Recent investigations on the production of plant food in 

the soil.— I. Roy. Hort. Soc. Jom-n. 4i:173-187. 1915 a. 

Same.— II. Roy. Hort. Soc. Journ. 41 : 188-199. 1915 b. 

Russell, Edward John, and Appleyard, Alfred. The atmosphere 
of the soil: its composition and the causes of variation. Journ. agr. 
sci. 7:1-48. 1915. 

The influence of soil conditions on the decomposition of 

organic matter in the soil. Journ. agr. sci. 8:385-417. 1917. 

SoRAUER, Paul. Der Einfluss der Luftfeuchtigkeit. Bot. Ztg. 36 : 1-13, 
17-25. 1878. 

Studien liber Verdunstung. Forsch. Geb. Agr.-Physik 3 : 351- 

490. 1880. 

Stoklasa, Julius. Methoden zur Bestimmimg der Atinimgsintensitat 
der Bakterien im Boden. Ztschr. landw. Versuchsw. Oesterreich 14: 
124.3-1279. 1911. 

Stoklasa, Julius, and Ernest, Adolf. Ueber den Ursprimg, die Menge, 
und die Bedeutung des Kohlendioxyds im Boden. Centbl. Bakt. 
2:14:723-736. 1905. 



The Carbon Dioxide of the Soil Air 351 

Beitrage zur Losuns; der Frage der chemischen Natur des 

Wurzelsekretes. Jahrb. wiss. Bot. [Pringsheim] 46:55-l'02. 1909. 

Suchtelen, F. H. Hesselink van. tJber die Messung der Leben- 
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reproduktioii. Centbl. Bakt. 2:28:45-89. 1910. 

WoLLNY, E. Untersuchungen iibsr den Einfiuss der Pflanzendecke und 

- der Beschattung auf den Kohlensauregehalt der Bodenluft. Forsch. 
Geb. Agr.-Physik 3 : 1-14. 1880 a. 

Untersuchungen uber den Kohlensauregehalt der Bodenluft. 

Landw. Vers. Stat. 25:373-391. 1880 b. 

Die Zersetzung der organischen Stoffe und die Humus- 



bildungen, p. 1-179. 1897. 

WoLLNY, Walter. Untersuchungen iiber den Einfiuss der Luftfeuchtig- 
keit auf das Wachsthum der Pflanzen, p. 1-44. Inaug. Diss., Halle. 
1898. 



The Caebojst Dioxide of the Soil Air 



353 



APPENDIX 

Carbon Dioxide (Per Cent by Volume) in Cropped and in XJncropped 
Soil (Oats, 1917) 



Temper- 


Atmos- 


ature 


pheric 


(centi- 


pres- 


grade) 


sure 




(inches) 


22 0° 


29. OG 


23.0° 


28.78 


23.0° 


28.98 


30.0° 


29.22 


21.0° 


29.12 


22.0° 


29.06 


23.0° 


29.02 


17.0° 


29.15 


21.5° 


29.16 


22.0° 


28.82 


30.0° 


28.88 


16.0° 


29.00 


21.0° 


29.05 


16.0° 


28.78 


17.0° 


28.77 


20.0° 


29.07 


29.0° 


29.27 


21.0° 


28.88 


22 0° 


29.10 


13.0° 


29.07 


22.0° 


29.17 


20.5° 


29.15 


30.0° 


29.55 


20.0° 


28.91 


28.0° 


28.92 


16.0° 


29.16 


24.0° 


28.95 


19.0° 


28.92 


30.0° 


29.14 


20.0° 


29.24 


35.0° 


29.05 


23.0° 


28.99 


35.0° 


28.93 


21.0° 


29.07 


25.0° 


29.22 


19.5° 


29.05 


26.0° 


29.21 


20.5° 


29.00 


32.0° 


28.97 


22.0° 


28.71 



Water 
added to 
maintain 
moisture 

content 

at 30 
per cent 

(grams) 



Carbon dioxide produced in 



Cropped 
soil 
(A) 



XJncropped 
soil 
(B) 



Difference 
(A-B) 



1.75 

2.75 

3.00 

4.50 

3.75 

2.50 

5.75 

7.25 

11.00 

16.75 

14.00 

11.25 

14.50 

20.25 

15.75 

23.75 

20.75 

27.00 

20.50 

31.25 

27.00 

39.50 

24.00 

'25'00 
20.00 
16.00 
7.50 
8.00 
6.00 
3.50 
6.00 
3.50 
1.50 
2.75 
1.25 



0.2S5±;009 

0.909±.017 

0.526±.007 

0.741±.019 

0.698±.017 

0.813±.013 

0.737±.014 

0.640±.013 

0.943±.027 

0.931±.037 

1.422±.048 

1.16G±.047 

1.034±.037 

1.307±.040 

1.297±.034 

2.031±.102 

1.708±.0e0 

1.982±.101 

1.365±.042 

1.292±.024 

1.315±.025 

1.809±.030 

1.412±.033 

1.846±.028 

1.778±.032 

0.799 

1.614d=.014 

1.699±.018 

1.7S1±.052 

1.111±.016 

1.595±.030 

1.261±.044 

1.475±.029 

1.040±.032 

1.028±.02S 

0.706±.012 

0.876±.012 

0.781±.019 

0.909±.012 

0.765±.013 



0.281±.006 
0.777±.014 
0.498±.009 
0.736±.003 
0.653±.004 
0.714±.008 
O.6.53±.007 
0.559±.007 
0.776±.009 
0.632±.006 
0.87S±.015 
0.475±.003 
0.452±.003 
0.415±.004 
0.477±.002 
0.648±.007 
0.698±.011 
O.530±.0O2 
0.452±.005 
0.416±.002 
0.419±.007 
0.4SO±.009 
0.466±.007 
0.496±.003 
0.620±.008 
0.393±.002 
0.449±.008 
0.394±.001 
0.633±.007 
0-.491±.005 
0.954±.015 
0.686±.007 
0.959±.007 
O.643±.O07 
0.629 ±007 
0.425±.003 
0.581±.005 
0,478±,003 
0.704±.002 
0.526±.007 



0.004±.011 
0.132±.022 
02S±.011 
0.005±.019 
0.045±.017 
0.099±.015 
O.OS4±.016 
0.081±.015 
0.167d=.028 
0.299±.037 
0.544±.050 
0.691±.047 
0.5S2±.037 
0.S92±.040 
0.820d=.034 
1.3S3±.102 
1.010±.060 
1.452±.101 
0.913±.043 
0.876±.024 
0.896±.02e 
1.329±.032 
0.946±.034 
1.350±.02S 
1.15S±.033 

'i'.165±'6i6 
1.305±.018 
1.148±.052 
0.620±.O17 
0.641±.033 
0.575±.044 
0.516± 030 
0.397±.032 
0.399=t,029 
0.281±-012 
0.295±.O13 
0,303± 019 
0,205±.012 
0.239±.015 



354 



H. W. TUEPIN 









TABLE 


1 (concluded) 








Temper- 
ature 
(centi- 
grade) 


Atmos- 
pheric 
pres- 
sxu-e 
(inches) 


Water 
added to 
maintain 
moistm-e 

content 

at 30 

per cent 

(grams) 


Carbon dioxide produced in 




Date 

of 

sampHng 


Cropped 
soli 
(A) 


Uncropped 
soil 
(B) 


Difference 
(A-B) 


August 27 
August 31 
Sept. 3 
Sept. 7 
Sept. 10 
Sept. 14 
Sept. 17 
Sept. 21 
Sept. 24 
Sept. 28 
Oct. 5 
Oct. 19 
Nov. 2 
Nov. 16 
Nov. 30 
Dec. 14 • 


29.5° 
14.0° 
25.0° 
14.0° 
14.5° 
15.5° 
25.0° 
18.0° 
24.0° 
18.0° 
16.0° 
24.0° 
17.0° 
19.0° 
17.0° 
17.5° 


29.20 
.29.37 
29.21 
29.23 
29.34 
29.41 
29.31 
29.06 
29.40 
28.93 
28.89 
28.92 
29.40 
29.08 
29.15 
28.69 




0.729±.009 
0.345±.007 
0.659±.015 
0.376±.007 
O.2S9±.O04 
0.3S5±.010 
0.544±.008 
0.554±.010 
0.415±.003 
0.495±.012 
0.309±.010 
0.404±.010 
0.382±.008 
0.424±.013 
0.280±.008 
0.356±.020 


0.538±.005 
0.244±.001 
0.488±.001 
O.256±.O03 
0.195±.003 
0.255±.007- 
0.378±.004 
0.348±.005 
0.266±.003 
0.328±.003 
0.211dz.004 
0.288±.006 
0.259±.004 
0.301±.016 
0.192±.005 
0.216±.007 


0.191±.010 
0.101±.O08 
0.171±.015 
0.120±.008 
0.094±.005 
O.1.30±.O13 
0.166±.009 
0.206±.011 
0.149±.004 
0.167±.013 
0.098±.011 
0.116±.011 
0.123±.009 
0.123±.021 
0.0S8±.010 
0.140±.021 



The Carbon Dioxide of the Soil Air 



355 



Carbon Dioxide (Per Cent by Volume) in Cropped and in Uncropped 
Soil (Oats, 1918) 









Water 














added to 


Carbon dioxide produced in 






Temper- 
ature 


Atmos- 
pheric 


maintain 
moisture 








Date 




• 


Difference 


of 


(centi- 


pres- 


content 


Cropped 


Uncropped 


(A-B) 


sampling 


grade) 


sure 


at 30 


soil 


soil 








(inches) 


per cent 
(grams) 


(A) 


(B) 




Jan. 3 


18.0° 


29.24 




0.373±.020 


0.229±.005 


0.144±.021 


Jan. 16 


18.5° 


28.84 




0.348±.014 


0.162±.002 


0.184±.014 


Jan. 31 


18.0° 


29.32 




0.315±.009 


O.223±.006 


0.092±.011 


Feb. 7 


20.0° 


29.20 




0.318±.010 


0.225±.002 


0.092±.010 


Feb. 11 


20.0° 


28.98 




0.340±.010 


0.249±.009 


0.091±.013 


Feb. 14 


22 5° 


28.97 




0.401±.010 


O.255±.009 


0.146±.013 


Feb. 18 


18.0° 


29.68 




0.370±.010 


' 0.221±.006 


0.149±.012 


Feb. 21 


20.0° 


28.75 


"".5!00 


0.509±.014 


0.258±.008 


0.251±.016 


Feb. 25 


20.5° 


28.83 


3.75 


0.445±.009 


0.195±.008 


0.250±.011 


Feb. 28 


20.0° 


29.25 


5.00 


0.595±.010 


0.240±.008 


0.355±.012 


March 4 


16.0° 


29.34 


5.75 


0.695±.016 


0.236±.008 


0.459±.018 


March 7 


20.0° 


28.96 


3.25 


0.639±.017 


O.295±.O07 


0.344±.018 


March 11 


16.0° 


29.54 


9.75 


0.834±.010 


0.236d=.008 


0.598±.020 


March 14 


20.0° 


28.48 


9.75 


0.989±.029 


0.223±.006 


0.743±.029 


March 18 


18.0° 


29.15 


14.25 


1.688±.027 


0.285±.006 


1.403±.028 


March 21 


25.0° 


28.88 


19.75 


2.290±.030 


0.471±.012 


1.819±.032 


March 25 


18.0° 


28.84 


24.00 


2.103±.030 


0.259±.009 


1.844±.031 


March 28 


21.0° 


29.39 


17.. 50 


2.224rh.055 


0.319±.010 


1.905±.056 


April 1 


21.0° 


28.81 


30.75 


2.514±.039 


0.331±.010 


2.183±.041 


April 4 


20.0° 


29.08 


27.00 


2.314±.033 


0.318±.003 


1.996±.034 


April 8 


19.0° 


29.39 


33.25 


1.855±.025 


O.17O±.O09 


1.695±.026 


April 11 


20.5° 


29.26 


14.00 


3.129±.033 


0.188±.004 


2.941±.034 


April 15 


20.5° 


29.22 


22.25 


2.704±.072 


0.320±.006 


2. 384 ±.072 


AprU IS 


24.0° 


28.83 


29.75 


2.580±.OS5 


0.311±.004 


2.239±.0S5 


April 22 


21.0° 


28.68 


24.25 


2.129±.089 


0.211±.005 


1.918±.0S9 


April 25 


'23.5° 


29.28 


15.00 


2.678±.056 


0.303±.006 


2.375±.057 


AprU 29 


22.5° 


28.97 


38.50 


2.418±.040 


0.238±.005 


2.182±.041 


May 2 


23.5° 


29.20 


21.00 


2.0o9±.046 


0.211±.003 


1.858±.046 


May 6 


23.0° 


29.07 


31.00 


3.343±.029 


0.3S9±.003 


2.954±.029 


May 9 


27.0° 


28.93 


30.25 


2.741±.041 


0..345±.004 


2.398±.041 


May 13 


23.0° 


28.92 


24.25 


2. 643 ±.045 


0.296d=.004 


2.347±.045 


May 16 


■ 27.5° 


29.41 


21.00 


2.753±.071 


0.283±.004 


2.487±.071 


May 20 


22.0° 


29.12 


23.00 


2.600±.O81 


O.276±.O04 


2.324±.081 


May 23 


24.0° 


29.30 


17.75 


2.934±.044 


0.295±.008 


2.639±.044 


May 27 


21.5° 


29.05 


17.25 


2.153±.065 


0.259±.008 


1.894±.065 


May .30 


23.5° 


29.17 


16.75 


1.51S±.018 


0.234±.005 


1.254±.018 


June 3 


20.5° 


29.19 


27.00 


2.045±.011 


0.344±.005 


1.701±.O12 


June 6 


22.5° 


29.10 


18.25 


1.331±.015 


0.299±.095 


1.062±.015 


June 10 


17.5° 


29.11 


17.75 


1.120±.017 


O.199±.003 


0.921±.017 


June 13 


21.5° 


28.77 


10.75 


1.070±.017 


0.220±.004 


0.850±.018 


June 17 


19.5° 


29.03 


15.59 


1.170±.007 


0,271±.095 


O.899±.O09 


June 20 


24.0° 


29.21 


11.75 


1.001±.OD9 


0.249±.002 


0.755±.009 


June 24 


14.0° 


29.00 


5.50 


0.519±,007 


0.140d=.002 


0.379±.007 



356 



H. W. TUHPIN 



TABLE 2 {concluded) 





Temper- 
ature 
(centi- 
grade) 


Atmos- 
pheric 
pres- 
sure 
(inches) 


Water 
added to 
maintain 
moisture 

content 

at 30 
per cent 

(gram.s) 


Carbon dio.xide produced in 




Date 

of 

sampling 


Cropped 
soil 
(A) 


Uncropped 
soil 
(B) 


Difference 
(A-B) 


June 27 
July 1 
July 4 
July 8 
July 11 
July 15 
July 18 
July 22 
July 25 
July 29 
August 1 
August 5 
August 8 
August 12 
August 14 
August 15 
August 16 
August 17 
August 19 
August 21 
August 22 
August 23 
August 24 
August 26 
August 27 


28.0° 
20.5° 
28.5° 
17.0° 
21.5° 
19.0° 
30.0° 
23.0° 
30.0° 
24,0° 
30.0° 
21.0° 
35.0° 
23.5° 
28.0° 
31.0° 
32.0° 
29.5° 
26.5° 
33.0° 
33.0° 
33.0° 
34.0° 
30.5° 
30.0° 


29.06 
28.84 
29.33 
28.99 
29.12 
29.12 
28.94 
29.31 
29.22 
29.14 
29.07 
28.92 
29.03 
29.16 
29.07 
29.21 
29.16 
29.50 
29.53 
29.21 
29.17 
29.10 
29.02 
28.96 
29.28 


6.00 
5.25 


1.169±.019 
1.500±.041 
1.026±.014 
0.763±.040 
0.745±.024 
1.028±.01S 
1.430±.040 
1.778±.004 
1.648d=.035 
1.788±.001 
1.020±.O38 
O.653±.O08 
1.563±.013 
1.0S8±.02S 
1.315±.007 
0.S85±.024 
0.835±.016 
0.760±.021 
0.688±.006 
0.715±.026 
0.8SS±.013 
0.988±.004 
1.145±.005 
0.7SS±.016 
O.6SS±.006 


0.396±.003 
0.369±.006 
0.336±.005 
0.215±.002 
0.295±.007 
0.333±.004 
0.578±.011 
0.750±.021 
0.895±.017 
0.92Q±.021 
0.580±.029 
0.375±.017 
0.920±.036 
0.635±.012 
0.790±.026 
0.525±.021 
0.505±.021 
0.478±.023 
0.400±.014 
0.430±.010 
0.588±.018 
0.633±.014 
0.695±.007 
0.468±.006 
0.448±.020 


0.773±.019 
1.131±,041 
0.690±.015 
0.548±.040 
0.450±.025 
0.695±.019 
0,852±.042 
1.028±.021 
0.753±.039 
0.868±.021 
0.440±.048 
0.278±.018 
0.643±.038 
0.423±.030 
0.525±.027 
0.360±.032 
0.330±.028 
0.282±.031 
0.268±.015 
0.285±.028 
0.300±.022 
0.355±.015 
0.450±.009 
0.320±.018 
0.240±.021 



The Carbon Dioxide of the Soil Air 



357 



TABLE 3. Relation between the Carbon Dioxide in the Cropped Soil during 
THE Period of Most Active Plant Growth, and the Water Transpired 
Each Week (Oats, 1917) 



Date 



Water 
trans- 
pired 
(grams) 



Total 
water 
trans- 
pired 
each 
week 
(grams) 
(A) 



Cropped soil 



Carbon 

dioxide 

(per cent) 

(B) 



Average 

carbon 

dioxide 

for the 

week 

(per cent) 

(C) 



Uncropped soil 



Carbon 

dioxide 

(per cent) 

(D) 



Average 

carbon 

dioxide 

for the 

week 

(per cent) 

(E) 



Difference 
in carbon, 

dioxide 

C-E 



Per cent of carbon 
dioxide to each 
pound of water 



_F 
A _ 
(G) 



C 

A 
(H) 



May 7. . 
May 11. 
May 14. 
May IS . 
May 21 . 
May 25 . 
May 28. 
June 1 . . 
.Tune 4 . . 
June 8 . . 
June 11. 
June 15 . 
June 18 . 
June 22 . 
June 25 . 
June 29 . 
July 2 . . 
July 6 . . 
July 9 . . 
July 13. 



5.75 1 
7.25 
11.00 1 
16.75 I 
14.00 1 
11.25 I 
14.50 1 
20.25 I 
15.75 1 
23.75 
20.75 1 
27.00 I 
20.50 1 
31.25 I 
27.00 1 
39.50 
24.00 1 

25!66 1 
20 . 00 ] 



13.00 
27.75 
25.25 
34.75 
39.50 
47.75 
51.75 
66.30 



0.943 1 

0.931 ■ 

1.422 

1.166 

1.034 

1.314 



297 
031 J 
7081 
982 J 
365 1 
292 I 
315 I 
809 I 
412 1 
846] 
778 1 



1.614 
1.699 



0.937 
1.294 
1.174 
1.664 
1.845 
1.329 
1.562 
1.629 

1.657 



0.7761 
. 632 J 
0.878 1 
0.475 J 
0.452 1 
0.415 J 
0.4771 
0.648 
0.698 
0.530, 
0.452 
0.410, 
0.419 
0.480, 
0.466' 
0.496 , 
0.620 1 
0.393 I 
0.449 1 
0.394 



0.704 
0.677 
0.434 
0.563 
0.614 
0.434 
0.450 
0.481 
0.507 
0.422 



0.233 
0.617 
0.740 
1.101 
1.231 
0.895 
1.112 
1.148 

1.235 



0.018 
0.022 
0.029 
0,032 
0.031 
0.019 
0.021 
0.017 

0.027 



0.072 
0.047 
0.046 
0.048 
0.047 
0.028 
0.030 
0.024 



0.037 



Mean 

Standard deviation 

Coef&cient of variability. 



0.024 

t.0012 
0.0054 

±.0009 
22.5 

±3.74 



0.042 

±.0031 
0.0136 

± . 0022 
37.40 

±5.65 



358 



H. W. Ttirpin 



TABLE 4 Reiation between the Cabeon Dioxide in the Ckopped Soil during 
THE Pekiod of Most Active Plant Growth, and the Water Tkanspieed 
Each Week (Oats, 1918) 



Date 



March 4 
March 7 
March 11 
March 14 
March IS 
March 21 
March 25 
March 28 
April 1 
April 4 
April 8 
April 11 
April 15 
AprU 18 
AprU 22 
April 25 
April 29 
May 2 
May 6 
May 9 



Water 
trans- 
pired 
(grams) 



5.75 
3.25 
9.75 
9.75 
14.25' 
19.75 
24.00 
17.50 
30.75' 
27.00 
33.25' 
14.00 
22.25' 
29.75 
24.25 
15.00 
38.50' 
21.00 
31.00' 
30.25 



Total 
water 
trans- 
pired 
each 
week 
(grams) 
(A) 



9.00 
19.50 
34.00 
41.50 
57.75 
47.25 
52.00 
39.25 
59.50 
61.25 



Cropped soil 



Carbon 

dioxide 

(per cent) 

(B) 



0.695' 

0.639 

. 834 ' 

0.969 

1.688' 

2.290 

2.103 

2.224 

2.514' 

2.314 

1.865' 

3.129 

2.704' 

2.. 580 

2.129' 

2.678 

2.418' 

2.069 

3.343' 

2.741 



Average 
carbon 
dioxide 
for the 
weelc 
(per cent) 
(C) 



0.667 
0.902 
1.989 
2.164 
2.414 
2.497 
2.642 
2.404 
2.244 
3.042 



TJncropped soil 



Carbon 

dioxide 

(per cent) 

(D) 



0.236 

0.205 

0.236 

0.226 

0.285' 

0.471 

0.259' 

0.319 

0.331 

0.318 

0.170' 

0.1S8 

0.320 

0.311 

0.211 

. 303 

0.230' 

0.211 

0.389' 

0.345; 



Average 
carbon 
dioxide 
for the 
week 
(per cent) 
(E) 



0.266 
0.231 
0.378 
0.289 
0..325 
0.179 
0.316 
0.257 
0.224 
0.3G7 



Difference 
in carbon 

dioxide 

C-E 

(F) 



0.401 
0.671 
1.611 
1.875 
2.089 
2.318 
2.326 
2.147 
2.020 
2.675 



Per cent of carbon 
dioxide to each 
pound of water 



F 
A 
(G) 



Mean 

Standard deviation 

Coefficient of variability 



0.045 
0.034 
0.047 
0.045 
0.036 
0.049 
0.045 
0.055 
0.034 
0.044 



C 
A 
(H) 



0.043 

d=.0014 
0.0065 

±.0010 
15.1 

±2.32 



0.074 
0.046 
0.059 
0.052 
0.042 
0.053 
0.051 
0.C61 
0.038 
0.050 



0.053 

±.0022 
0.0102 

±.0015 
19.17 

±3.12 



TABLE 5. 



Relation between the Drt Weight of the Crop and the Carbon Dioxide 
Given Off by Pl.u^t Roots 
(From Stoklasa and Ernest, 1909) 



Cro-i 



Barley 

Rye 

Oats 

Wheat 

Average 



Total 

dry matter 

produced 

in 84 days 

(milligrams) 



34,493 
27,046 
28,215 
18,375 



26,532 



Total 

carbon dioxide 

produced 

in S4 days 

(milligrams) 



1,267 

1,053 

■793 

784 



974 



Milligrams of 
carbon dioxide 

produced to 
each milligrcm 
of dry matter 



0.037 
0.039 
0.030 
0.043 



0.037 



The Caebon Dioxide of the Soil Air 



359 



TABLE 6. Caebon Dioxide (Pee Cent by Volume) in Cropped and in Unceopped 

Soil (Millet, 191S) 



Date of 
sampling 



Carbon dioade produced in 



Series 1 (high CO2 soil) 



Cropped 
(per cent) 



Bare 
(per cent) 



Series 2 (low CO2 soil) 



Cropped 
(per cent) 



Bare 

(per cent) 



JulvS 

July 11 

July 15 

July 18 

July 22 

July 25 

July 29 

August 1. . . . 
August 5. . . . 
August 8. . . . 
August 12. . . 
August 14 . . . 
August 15. . . 
August 16. . . 
August 17. . . 
August 19... 
August 21. . . 
August 22. . . 
August 23. . . 
August 24. . . 
August 26. . . 
August 27. . . 
August 2S. . . 
August 29. . . 
August 31. . . 
September 3 



0.713±.016 
0.763±.006 
1.045±.031 
1.455±.O50 
1.803±.032 
2.015±.079 
1.923±.101 
1.305±.055 
1.133±.008 
2.115±.017 
2.025±.021 
2.448±.02S 
1.864±.016 
1.950±.010 
2.108±.018 
2.040=h.048 
2.288±.016 
3.098d=.023 
3.095±.OGO 
3.345±.0.35 
2.465±.O05 
2.198±.009 
2.245±.031 
2.093±.039 
1.9S3±.011 
1.770±.021 



0.763±.040 
0.745±.024 
1.02S±.018 
1.430±.040 
i.77S±.004 
1.648±.035 
1.788±.001 
1.020±.038 
O.653±.O06 
1.563±.013 
1.088±.028 
1.315±.007 
0.885±.024 
O.S35±.C16 
0.760±.021 
O.638±.005 
0.715±.026 
0.88S±.013 
0.9S8±.004 
1.145±.005 
0.7SS±.016 
0.6SS±.003 
0.690±.036 
0.613±.004 
0.590±.007 
0.533±.011 



0.210±.002 
O.283±.O01 
0.358±.001 
0.578±.001 
0.79o±.014 
0.908±.059 
1.008±.054 
0.798±.039 
0.750±.052 
1.62S±.161 
1.223±.018 
1.710±.043 
1.405±.012 
1.480±.033 
1.683±.049 
1.683±.()42 
1.948±.016 
2.655±.055 
2.715±.074 
2.690±.060 
2.27o±.064 
2.133±.075 
1.958±.056 
2.120±.088 
2.245±.114 
2.143±.068 



0.215±.002 
O.295±.O07 
0.333±.004 
O.578±.O01 
O.750±.O21 
0.895±.017 
0.920±.021 
0.580±.029 
0.375±.017 
0.920±.036 
0.665±.012 
0.790d=:.026 
0.525±.021 
0.505±.021 
0.478±.023 
0-400±.014 
0.430±.010 
0.5S8±.018 
0.633±.014 
0.695±.007 
0.468±.006 
0.448±.020 
0.348±.004 
O.358±.O06 
0.370±.010 
0.310±.005 



360 



H. W. TUBPIN 



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The Cakbon Dioxide of the Soil Air 



361 



TABLE 8. Cakbon Dioxide (Per Cent by Volume) Produced Appaeentlt by the 
Millet Crop, 191S. Determined by Subtracting the Amount op Carbon Dioxide 
IN the Bare Soil from That in the Cropped Soil 



Date 
of sampling 



July 8 

July 11... 
July 15... 
July 18... 
July 22... 
July 25. . . 
July 29..., 
August 1. . 
August 5. . 
August 8. . 
August 12. 
August 14. 
August 15. 
August 16. 
August 17. 
August 19. 
August 21. 
August 22. 
August 23. 
August 24. 
August 26. 
August 27. 
August 28. 



Carbon dio.xide apparently pro- 
duced by millet crop in 



High CO2 soil 

(I) 



— 
+0 
+0 
+0 
+0 
+0 
+0 
+0 
+0 
+0 
+0 

+1 

+0 

+1 
+1 
+1 
+1 

+2 
+2 
+2 
+ 1 
+ 1 
+1 



.050±.O43 
.018±.025 
.017±.O36 
.025±.064 
.025±.032 
.367±.0S6 
.135±.101 
.285±.067 
.480±.O0S 
.552±.021 
.937±.035 
.133±.029 
.979±.041 
.115±.019 
.348±.028 
.372±.048 
.573±.031 
.210±.026 
.107±.062 
.200±.01S 
.677±-01S 
.510±.011 
.555±.048 



Low CO2 soil 
(11) 



— 0.005±.003 
— 0.012±.007 
+0.02o±.004 
0.000±.015 
+0.04o±.025 
+0.013±.061 
+0.0S8±.058 
+0.218±.049 
+0.375±.055 
-|-0.708±.170 
+0.558 ±.022 
+0.920±.050 
+0.S80±.024 
+0.975±.O39 
+1.205±.054 
+ 1.283±.044 
+ 1.518±.019 
+2.067±.0oS 
+2.082±.O75 
+ 1.995±.O60 
+ 1.S07±.064 
+ 1.6S5±.077 
+ 1.610±.056 



Difference 
(I-II) 



— 0.045±.043 
+0.030±-028 
—0. COS ±.036 
4-0.025±.066 
— 0.020±.041 
+0.354±.106 
+0.047±.116 
+0.067±.0S2 
+0.105 ±.0.55 
^0.156±.167 
+0.379±.041 
+0.213±.058 
+0.103±.048 
+0.140±.047 
+0.143±.0G1 
+0.0S9±.066 
+0.055±.03o 
+0.143±.064 
+0.025±.096 
+0.205±.063 
— 0.130±.067 
— 0.175±.078 
— 0.055±.074 



362 



H. W. TURPIN 



TABLE 9. Cakbon Dioxide (Per Cent by Volume) in Chopped and in TJnceopped 
Soil of Low Initial Carbon-Dioxide Content (Millet, 1918) 



Date 
of sampling 



July S . . . . 
July 11... 
July 15. . . 
July 18... 
July 22. . . 
July 25... 
July 29... 
August 1. . 
August 5. . 
August 8. . 
August 12. 
August 14. 
August 15. 
August 16. 
August 17. 
August 19. 
August 21. 
August 22. 
August 23. 
August 24. 
August 26. 



Tem- 
perature 
(centi- 
grade) 



17.0° 
21.5° 
19.0° 
30.0° 
23.0° 
30.0° 
24.0° 
30.0° 
21.0° 
35.0° 
23.5° 
28.0° 
31.0° 
32.0° 
29.5° 
26.5° 
33.0° 
33.0° 
33.0° 
34.0° 
30.5° 



Atmos- 
pheric 
pressure 
(inches) 



28.99 
29.12 
29.12 
28.94 
29.31 
29.22 
29.14 
29.07 
28.92 
29.03 
29.16 
29.07 
29.21 
29.16 
29.50 
29.53 
29.21 
29.17 
29.10 
29.02 
28.96 



Carbon dioxide produced in 



Cropped soil 

(I) 



0.210±.002 
0.283±.001 
0.358±.001 
0.57S±.001 
0.795±.014 
0.908±.059 
1.008±.054 
0.798±.039 
0.750±.052 
1.62S±.161 
1.223±.018 
1.710±.O43 
1.405±.012 
1.480 ±.033 
1.683±.049 
1.683±.042 
1.94S±.016 
2.655±.055 
2.715±.074 
2.690±.060 
2.275±.064 



Uncropped soil 
(11) 



0.215±.002 



.007 
.004 



0.295± 

0.333± 

0.578±.001 

0.750±.021 

0.895±.017 

0.920±.021 

0.5S0±.029 

0.375±.017 

0.920±.036 

0.665±.012 

0.790±.026 

0.525±.021 

0.505±.021 

0.478±.023 

0.400±.014 

0.430±.010 

0.588±.018 

0.633±.014 

0.695±.007 

0.468±.006 



Difference 
(I-II) 



— 0.005±.003 
— 0.012±.007 
-|-0.025±.004 
0.000±.016 
4-0.045±.025 
-|-0.013±.061 
+0.088±.058 
-1-0,218±.049 
-|-0.375±.055 
-|-0.7O8±.17O 
-|-0.558±.022 
-f-0.920±.050 
-|-0.880±.024 
+0.975±.039 
-H.205±.054 
-M.2S3±.004 
-|-1.518±.019 
-|-2.067±.058 
-|-2.0S2±.075 
-|-1.995±.060 
-|-1.807±.064 



Memoir 29, The Lecithin Content of Butter and Its Possible Relationship to the Fishy Flavor, the third pre- 
ceding aumber in ttiis series of publications, was mailed on December 23, 1919. 



I 



LIBRARY OF CONGRESS 



e 002 683 250 




